1. Field of the Invention
The present invention relates to a cooling structure for an internal combustion engine in which: a spacer is fitted inside a water jacket formed to surround a periphery of a cylinder bore of a cylinder block in the internal combustion engine; and a cooling condition of the cylinder bore is controlled by regulating a flow of cooling water in the water jacket by use of the spacer.
2. Description of the Related Art
Japanese Patent Application Laid-open No. 2005-273469 has made publicly known such a cooling structure for an internal combustion engine in which: assuming that the space formed between the internal peripheral surface of the spacer and the inner wall surface of the water jacket is divided into an upper region, an intermediate region and a lower region in a cylinder axis line direction, the spaces in the upper region and the lower region are set larger than the space in the intermediate region; and thereby, the cylinder bores are cooled uniformly in the cylinder axis line direction.
Meanwhile, such a spacer is fitted inside the water jacket, and regulates the flow of the cooling water, hence controlling the cooling condition of the cylinder bores. Thereby, the spacer exerts an effect of reducing friction between each piston and the corresponding cylinder bore. In this regulation, however, if the spacer excessively restricts the flow of the cooling water in the upper and lower portions of the water jacket in the cylinder axis line direction, heat may be insufficiently dissipated from the upper and lower portions of each piston to the cylinder bore, and seizure of the piston and the like may occur. Particularly, the upper portion of each piston is in contact with the cylinder bore with its piston ring interposed in between. For this reason, the performance of heat dissipation from the upper portion of each piston to the cylinder bore needs to be secured.